Various methods and compositions for targeted cleavage of genomic DNA have been described. Such targeted cleavage events can be used, for example, to induce targeted mutagenesis, induce targeted deletions of cellular DNA sequences, and facilitate targeted recombination at a predetermined chromosomal locus. See, e.g., U.S. Pat. Nos. 8,586,526; 8,329,986; 8,399,218; 6,534,261; 6,599,692; 6,503,717; 6,689,558; 7,067,317; 7,262,054; 7,888,121; 7,972,854; 7,914,796; 7,951,925; 8,110,379; 8,409,861; U.S. Patent Publications 20030232410; 20050208489; 20050026157; 20050064474; 20060063231; 20080159996; 201000218264; 20120017290; 20110265198; 20130137104; 20130122591; 20130177983 and 20130177960 and U.S. application Ser. No. 14/278,903, the disclosures of which are incorporated by reference in their entireties for all purposes.
These methods often involve the use of engineered cleavage systems to induce a double strand break (DSB) or a nick in a target DNA sequence such that repair of the break by an error born process such as non-homologous end joining (NHEJ) or repair using a repair template (homology directed repair or HDR) can result in the knock out of a gene or the insertion of a sequence of interest (targeted integration). Cleavage can occur through the use of specific nucleases such as engineered zinc finger nucleases (ZFN), transcription-activator like effector nucleases (TALENs), using the CRISPR/Cas system with an engineered crRNA/tracr RNA (‘single guide RNA’) to guide specific cleavage and/or using nucleases based on the Argonaute system (e.g., from T. thermophilus, known as ‘TtAgo’, (Swarts et at (2014) Nature 507 (7491): 258-261).
Targeted cleavage using one of the above mentioned nuclease systems can be exploited to insert a nucleic acid into a specific target location using either HDR or NHEJ-mediated processes. However, delivering both the nuclease system and the donor to the cell can be problematic. For example, delivery of a donor or a nuclease via transduction of a plasmid into the cell can be toxic to the recipient cell, especially to a cell which is a primary cell and so not as robust as a cell from a cell line.
CD34+ stem or progenitor cells are a heterogeneous set of cells characterized by their ability to self renew and/or differentiate into the cells of the lymphoid lineage (e.g. T cells, B cells, NK cells) and myeloid lineage (e.g. monocytes, erythrocytes, eosinophiles, basophiles, and neutrophils). Their heterogeneous nature arises from the fact that within the CD34+ stem cell population, there are multiple subgroups which often reflect the multipotency (whether lineage committed) of a specific group. For example, CD34+ cells that are CD38− are more primitive, immature CD34+ progenitor cell, (also referred to as long term hematopoietic progenitors), while those that are CD34+CD38+ (short term hematopoietic progenitors) are lineage committed (see Stella et al (1995) Hematologica 80:367-387). When this population then progresses further down the differentiation pathway, the CD34 marker is lost. CD34+ stem cells have enormous potential in clinical cell therapy. However, in part due to their heterogenous nature, performing genetic manipulations such as gene knock out, transgene insertion and the like upon the cells can be difficult. Specifically, these cells are poorly transduced by conventional delivery vectors, the most primitive stem cells are sensitive to modification, there is limited HDR following induced DNA DSBs, and there is insufficient HSC maintenance in prolonged standard culture conditions. Additionally, other cells of interest (for non-limiting example only, cardiomyocytes, medium spiny neurons, primary hepatocytes, embryonic stem cells, induced puripotent stem cells and muscle cells) can be less successfully transduced for genome editing than others.
Thus, there remains a need for compositions and methods for genome engineering to CD34+ cells and other cells of interest that are less toxic and more efficient.